qlcnic: dcb: Query adapter DCB capabilities.

o Query adapter DCB capabilities and  populate local data structures
  with relevant information.

o Add QLCNIC_DCB to Kconfig for enabling/disabling DCB.

Signed-off-by: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>